1. Field of the Invention
The present invention relates to a combined sensor and bearing assembly installed in any of various machines and equipments for detecting the rotation of a rotating mechanism within, for example, a limited range of angle, and a method of magnetizing a rotation sensor unit employed in the combined sensor and bearing assembly.
2. Description of the Related Art
The rotation sensor unit used in the combined sensor and bearing assembly has been well known in the art from, for example, the Japanese Laid-open Patent Publications No. 2004-004028 and No. 2004-20548, in which along with the rotation of a rotatable race two, 90° phase offset sinusoidal outputs are obtained in the form of a sine wave signal and a cosine wave signal so that the tangent value can be obtained from those signals to detect the absolute position of rotation angle of the rotatable race.
Also, irrespective of the bearing, an independent magnetic angle detecting device is known, which includes a magnetic sensor unit of an analog output type mounted on a stationary member and a magnet, which is a to-be-detected member, mounted on a rotating member in face-to-face relation with the magnetic sensor unit so that an analog output proportional to the angle of rotation of the rotating member can be obtained as the to-be-detected member rocks or rotates with the rotating member. See, for example, the Japanese Laid-open Patent Publication No. 8-122011.
It has, however, been found that the system in which the absolute position of the angle of rotation is detected based on the two 90° phase offset sinusoidal outputs, requires the use of an extra signal processing circuit for processing the detection signal. Positioning of the signal processing circuit adjacent the rotation sensor unit is difficult to achieve because of a limited space available and an additional problem is involved in designing in a compact size the machine in which the combined sensor and bearing assembly is incorporated. With the combined sensor and bearing assembly having built therein a sensor for detecting the absolute position, the angle of rotation is often limited to a certain range, for example, not larger than 180°, depending on the condition of use. In this case, there is no need to use the two sensor outputs to detect the angle of rotation.
In the system in which the magnet disposed in face-to-face relation with the magnetic sensor rotates or rotates within a limited range of angle such as the magnetic angle detecting device disclosed in the third mentioned patent publication, in order for the sensor output to exhibit a linear characteristic within a predetermined range of angle of rotation, it is necessary for the magnet to be magnetized to represent as closely a sinusoidal waveform as possible. However, the third mentioned patent publication is silent as to the details of magnetization. Although magnetization with an air-core coil is well known in the art, the magnetic field used therein lacks stability and, therefore, difficulty has been encountered with to magnetize the magnet to represent a magnetic intensity distribution resembling the sinusoidal waveform. Also, what is disclosed in the third mentioned patent publication is a mere magnetic angle detecting device and no rolling bearing assembly for rotatably supporting a shaft member is employed therein and, accordingly, there is a high risk that the precision may lower as a result of a mechanical frictional wear occurring in an insertion hole or the like for the passage of a shaft member of a housing therethrough even though the sensor unit is designed to be of a non-contact type.